Methods of coating implantable leads

ABSTRACT

An implantable cardiac lead, and/or subassembly includes an elongate sheath of insulative material including an insulative first layer and a protective second layer. The insulative first layer has at least one activated surface to which the protective second layer is coupled.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.10/889,504, filed on Jul. 12, 2004, the specification of which isincorporated herein by reference.

TECHNICAL FIELD

The present subject matter relates to leads for stimulating ormonitoring tissue. More particularly, it pertains to methods of coatingsuch leads.

BACKGROUND

Leads implanted in or about the heart have been used to reverse certainlife threatening arrhythmias, or to stimulate contraction of the heart.Electrical energy is applied to the heart via the leads to return theheart to normal rhythm. Leads have also been used to sense in the atriumor ventricle of the heart and to deliver pacing pulses to the atrium orventricle.

The lead includes one or more conductors to conduct energy from thepacemaker to the heart, and also to receive signals from the heart. In atypical construction, one conductor goes to the band electrodeproximally (outer electrode) and another conductor goes to the tipelectrode at the distal end (inner electrode). The conductors run sideby side and are insulated from each other and also from the body. Theinsulation is typically a polymer tubing or covering over the lead body.These polymeric materials must demonstrate resistance to hydrolysis anddegradation by oxides found in the body. These polymeric materials mustalso demonstrate appropriate mechanical and electrical properties foruse as electrical stimulation leads.

Silicone rubber and polyurethanes have been used most commonly toinsulate leads. The silicone rubbers have excellent biocompatibility andlong-term stability but they have weak tensile strength and low abrasionresistance. Polyurethanes are less thrombogenic than silicone rubber andhigher in tensile strength. In addition, they slide easily against oneanother when moistened with body fluids. However, polyurethanes tend tobe stiffer and not as pliable as silicone rubber.

Currently, leads are sometimes manufactured with a proximal polyurethanesection and a distal silicone section. To achieve the requiredinsulative properties, separate silicone and polyurethane compositetubing are layered over the lead.

Accordingly, there is a need for a lead insulation that has flexiblematerial resistance and has improved lubricity.

SUMMARY

An implantable cardiac lead is provided that includes an elongate sheathof an insulated first layer of material, where the elongate sheathextends from a proximal end to a distal end and includes an intermediateportion therebetween. The elongate sheath is defined in part by an outersurface and an inner surface. An elongate conductor is located withinthe elongate sheath, and an electrical connector is coupled to theconductor. The insulating first layer includes an adhesive enhancingactivated surface.

Several options for the implantable cardiac lead are as follows. Forinstance, in one option, the adhesive enhancing activated surface ismanufactured via plasma assisted chemical vapor deposition treatment,for instance with the monomers including but not limited to acrylicacid, allyl amine, acrylamide, acrylonitrile, methacrylic acid, glycidylmethacrylate, N,N-dimethylacrylamide, and acetylene. In another option,the adhesive enhancing activated surface is manufacture via chemicaltreatment. In another option, the activated surface includes a recessportion, and a second layer of material is disposed within the recessportion. In yet another option, the lead further comprises a terminalarea with a connector, and a second layer of material is applied to theterminal area of the lead.

In another option, an implantable cardiac lead subassembly is providedthat includes an elongate flexible body extending from a proximal end toa distal end and defined in part by an outer surface and an innersurface. In one option, at least a portion of the outer surface or theinner surface has an activated surface that is covered by a secondcoating of material, such as polyurethane. Further options includeproviding first and second layers of material that transition from acombination of polyurethane and silicone to silicone only.

In another embodiment, a method is provided that includes providing aflexible lead body having a surface, an increasing adhesion of thesurface including activating the surface of the flexible lead body. Themethod further includes coating a second layer of material, such as aprotective material on the activated surface of the flexible lead body.

Several options are as follows. For instance, the method furtherincludes activating the surface of the flexible lead body using plasmaassisted chemical vapor deposition, or treating the surface of theflexible lead body with a monomer. In one option, the monomer includesat least one of acrylic acid, allyl amine, acrylamide, acrylonitrile,methacrylic acid, glycidyl methacrylate, N,N-dimethylacrylamide, andacetylene. Subsequent processing may include coating the surface with atleast one of polyurethane and silicone. In yet another option thecoating is disposed along only a portion of the lead body. In yetanother option the coating is coated only on a distal area of a flexiblelead body.

These and other embodiments, aspects, advantages, and features of thepresent invention will be set forth in part in the description whichfollows, and in part will become apparent to those skilled in the art byreference to the following description of the invention and referenceddrawings or by practice of the invention. The aspects, advantages, andfeatures of the invention are realized and attained by means of theinstrumentalities, procedures, and combinations particularly pointed outin the appended claims and their equivalents.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a block diagram of a lead assembly constructed inaccordance with an embodiment.

FIG. 2A illustrates a cross-sectional view of a portion of a leadassembly constructed in accordance with at least one embodiment.

FIG. 2B illustrates a cross-sectional view of a portion of a leadassembly constructed in accordance with at least one embodiment.

FIG. 2C illustrates a cross-sectional view of a portion of a leadassembly constructed in accordance with at least one embodiment.

FIG. 3 illustrates a flow diagram for a method in accordance with atleast one embodiment.

FIG. 4 illustrates an elevational view of a lead constructed inaccordance with at least one embodiment.

FIG. 5 illustrates a side-elevational view of a portion of a leadconstructed in accordance with at least one embodiment.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments in which the invention maybe practiced. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention, and it is tobe understood that other embodiments may be utilized and that structuralchanges may be made without departing from the scope of the presentinvention. Therefore, the following detailed description is not to betaken in a limiting sense, and the scope is defined by the appendedclaims.

A lead assembly 110 and lead system 100 are illustrated in FIG. 1. FIG.1 is a diagram of a system 100 for delivering and/or receivingelectrical pulses or signals to stimulate, shock, and/or sense the heart102. The system 100 includes a pulse generator 105 and a lead 110. Thepulse generator 105 includes a source of power as well as an electroniccircuitry portion. The pulse generator 105, in one option, is abattery-powered device which generates a series of timed electricaldischarges or pulses. The pulse generator 105 is generally implantedinto a subcutaneous pocket made in the wall of the chest. Alternatively,the pulse generator 105 is placed in a subcutaneous pocket made in theabdomen, or in other locations. It should be noted that while the leadassembly 110 is illustrated for use with a heart, the lead assembly 110is suitable for other forms of stimulation as well. For example, thelead assembly 110 can be used for neurostimulation.

The lead assembly 110 includes a lead body 113 which extends from aproximal end 112, where it is coupled with the pulse generator 105, asfurther discussed below. The lead assembly 110 extends to a distal end114, which is coupled with a portion of a heart 102, when implanted orotherwise coupled therewith. Disposed along a portion of the lead body113, for example near the distal end 114 of the lead assembly 110includes at least one electrode assembly 116 which electrically couplesthe lead assembly 110 with the heart 102. At least one electricalconductor 118 (FIG. 2A) is disposed within the lead assembly 110 andextends, in one option, from the proximal end 112 to the distal end 114of the lead assembly 110. The at least one electrical conductor 118electrically couples the electrode assembly 116 with the proximal end112 of the lead assembly 110. The electrical conductors carry electricalcurrent and pulses between the pulse generator 105 and the electrodeassembly 116, and to and from the heart 102. In one option, the at leastone electrical conductor 118 is a coiled conductor. In another option,the at least one electrical conductor 118 includes one or more cables.

FIGS. 2A, 2B, and 2C illustrate cross-sectional views of a portion ofthe lead body including a first layer of material 120. The lead body 113further includes a second layer of material 117. The first layer ofmaterial 120, in one option, forms an insulative body to the lead. Thefirst layer of material 120 is defined in part by an outer surface 108and inner surface 106. In one option, the second layer of material 117is disposed along only a portion, or continuously along an outer surface108 of the first layer of material 120 to form the lead body 113, asillustrated in FIG. 2A. In another option, the second layer of material117 is disposed along only a portion, or continuously along a length ofthe lead of the inner surface 106 of the first layer of material 120 toform the lead body 113, as illustrated in FIG. 2B. In yet anotheroption, the first layer of material 120 of the lead body includes avariable outer diameter such as that shown in FIG. 2C.

In one option, the second layer of material 117 is disposed within arecess of the first layer of material 120. The recess 115 is formed, inone option, in an outer surface 108 of the first layer of material 120of the lead body 113. The recess 115, in an option is treated with theadhesive enhancing surface 121, and allows for a coating of material,such as polymeric material therein. The recess 115 allows for the outerdiameter, or portions of the outer diameter, to be coated with material,such as polyurethane or other materials, and yet further allows for theouter body to be formed isodiametrically. The recess 115 can be formedin a number of different manners. For example, the recess 115 can beformed using a die-stretching process.

The first layer of material 120 of the lead body, in one option,includes one or more activated surfaces 121. The activated surface 121of the first layer of material 120 allows for the adhesiveness to beenhanced and allowing for coating of a second protective layer ofmaterial, for example, polymeric material to be coated thereon. Theadhesive enhancing activated surface allows for two normally dissimilarsubstances to be coupled without the use of adhesive. The activatedsurface can be formed on the outer surface, and/or an inner surface,and/or portions along the outer and/or inner surfaces, and/or withinrecesses within either the outer surface and/or the inner surface of thefirst layer of material 120.

The activated surface of the first layer of material 120 can beactivated in a number of different manners. In one option, the adhesiveenhancing activated surface of the first layer of material 120 isproduced by plasma surface modification or by plasma assisted orenhanced chemical vapor deposition treatment. The plasma treatmentinvolves a number of steps. For example, the plasma treatment includesan optional first step of cleaning the surface to be activated, forexample, at an atomic level. Suitable gases for the pre-cleaning processinclude, but are not limited to, O₂, Ar, N₂, CH₃OH, and CF₄. The plasmatreatment further includes a plasma deposition process with a gas, toform a tie layer. The plasma treatment further includes another stepinvolved in the plasma enhanced deposition. This process involvesfunctionalizing the surface, and thereby activating the surface, of thefirst layer of material 120 to increase the adhesiveness to thatsurface. Suitable monomers for treating the surface include but are notlimited to, acrylic acid, allyl amine, acrylamide, acrylonitrile,methacrylic acid, glycidyl methacrylate, N,N-dimethylacrylamide, andacetylene.

The surface of the first layer of material 120 can be activated in otherdifferent manners, other than discussed above. For example, the adhesiveenhancing activated surface of the first layer of material 120 can beproduced by a chemical treatment to the first layer of material 120.

Once a surface of the first layer of material 120 has been activated,the first layer of material can be coated with a second layer ofmaterial, such as a polymeric material, for example, polyurethane. Thisprovides a protecting coating to the first layer of material 120, wherethe first layer of material 120 forms an insulative coating. The secondlayer of material 117 can be applied in number of different manners. Forexample, the second layer of material can be coated onto the first layerof material. Coating can include dip coating or spray coating but is notnecessarily so limited. Other examples of application include applying asecond layer of material such as polyurethane by a melt process, or byapplying with a tool such as a needle or brush, or spray coated.

Suitable materials for the first layer 120 and the second layer ofmaterial 117 are as follows. For example, the first layer of materialcan be formed of one or more of the following materials: siliconerubber, PTFE, ePTFE. The second layer of material 117 can be formed ofpolyurethane and/or other materials. In another option, the second layeris formed of a material that is more stiff than the first layer ofmaterial. The stiff changes can be disposed along all, a portion, orvarious portions of the lead. This allows for changes to the handlingattributes of the lead as the stiffness of the lead can be modifiedalong the lead. For example, an intermediate portion of the lead can bemade more stiff than a distal end, decreasing risk of inadvertentpenetration through a vessel wall or tissue. Furthermore, the handlingattributes of the lead can be modified, including, but not limited to,thickness changes of the lead body.

FIG. 3 illustrates a flow diagram showing one example of how enhancedadhesion of a first layer of material, is achieved. As discussed above,one or more surfaces of the first layer of material 120 are activated toenhance its adhesiveness. Several embodiments include, but are notlimited to, plasma surface modification, chemical treatment, and/orplasma assisted chemical vapor deposition treatment. It should be notedthat one or more of the above processes may be used to form theactivated surface. After the surface of the first layer of material isactivated to enhance adhesion, the activated surface is coated with asecond layer of material 117, such as a protective layer, for example,polyurethane. As discussed above, the coating can be done in a number ofmanners, including but not limited to spray coating, dip coating, orapplied by a melt process.

Some example methods are as follows:

EXAMPLE #1

Silicone tubing is activated by a plasma process and subsequent plasmaenhanced chemical vapor deposition of acrylic acid.

Next polyurethane solution is prepared using the following steps:

-   1. A flask is filled with dimethylacetamide (DMAC).-   2. Polyurethane (Pellethane 2363-55D) is added to the DMAC solution.-   3. The solution is stirred at a predetermined temperature, for a    predetermined time, where a refluxing condenser maintains the volume    of DMAC.-   4. After the polyurethane has fully dissolved, the polyurethane-DMAC    solution is removed from the flask.-   5. DMAC is added to the stock solution to create a polyurethane-DMAC    solution.

After preparing the solution the tubing can be dip coated. Thepreviously prepared tubing is cut to length and is placed on a dipcoater apparatus. This solution is transferred to a metal container andis used as the dipping container. The tubing is slowly cycled into andout of the polyurethane-DMAC solution. As or after the tubing comes outof the dipping solution, the tubing is subjected to heat.

Example #2

The same process is used as in example #1 except an acetone/DMACsolution is used.

Example #3

For spray coating, the same tubing preparation process can be used asdescribed in example #1 and #2. Likewise, the solution is still preparedas described in example #1 and #2. In this case, however, a lowerpercentage of polyurethane is used in the final solution. In the spraycoat process, the tubing is mounted on a mandrel. As the sprayer spraysthe solution over the tubing, the tubing is rotated horizontally tomaintain a uniform coating. Hot air is passed over the tubing to improveevaporation of the solvent during subsequent spray coats. Approximately100 passes of 1% polyurethane solution create a 1 mil thick coating.

Example #4

The dip coating process is performed as described in example #1.However, dimethylsulfoxide (DMSO) is used in place of DMAC.

Example #5

To decrease the number of required dips or spray cycles (and thusmanufacturing time) to achieve a given thickness coating, a higherpercentage of polyurethane can be used in the above examples. Tomaintain the same viscosity the solution can be heated.

FIGS. 4 and 5 illustrate examples of use of the first and second layersof material within medical devices such as leads. FIG. 4 illustrates aside elevational view of the lead 110 that extends from a proximal end112 to a distal end 114. In one option, the distal end 114 includes anactive fixation device such as a helix. In another option, the lead 110includes an electrode 116. The lead body 113, optionally, is formed sothat it transitions from a single layer of material, such as silicone,to a combination of materials, such as silicone and polyurethane. Thetransition assists in allowing the distal end of the lead to bepreformed in a variety of shapes, for example, without requiring the useof a wire. For example, the distal end 114 of the lead can be formed ina J-shape.

The lead body 113 can be formed in a subassembly such that the componentcan be partially formed and stocked to be used at a later date, orfurther processed at a later date. For example, a first layer ofmaterial 120 could be activated along the entire surface, or only alonga partial amount of the surface, and stocked for further use at a latertime. In another option, the entire first layer of material 120 can beactivated, and only a portion of the first layer of material 120 can becoated with a second layer of material 117, and can be stocked in thatform, to be used at a later date. In yet another option a distal portion132 of the lead 110 includes only a first layer of insulative material,such as silicone, such that the distal end 114 can remain much moreflexible than the remaining portions of the lead 110, which are coatedwith the protective layer of material 117. The distal portion 132 isdisposed adjacent to the distal end 114 of the lead 110.

In an embodiment, the lead 110 further includes a transition portionthat allows for the lead body to include portions with just the firstlayer of material 120 that transitions to a portion that includes acombination of the first layer of material 120 and the second layer ofmaterial 117. The transition portion is disposed along an intermediateportion 134 of the lead.

An intermediate portion 134 extends from the portion 132 to the proximalend of 112 of the lead. To form the transition portion, the first layerof material, such as silicone, is treated for example with theactivation processes discussed above. The first layer of material issprayed with a fine thin layer of polyurethane along the portion to formthe transition portion. The polyurethane is fixed to the first layer ofmaterial via heat, laser, etc. to create the transition.

In yet another option, the second layer of material 117 is applied tothe distal portion of the lead in order to facilitate creation of astructure, for example, such as a preformed J-shape or spiral shape.That is, the tubing formed by the first and second layers of materialsthemselves can be formed into a J-shape.

FIG. 5 illustrates a proximal portion of a lead 110, including aterminal end 140. The terminal end 140 includes a connector that isdisposed within a header of a pulse generator (FIG. 1) disposed adjacentto the terminal portion is a portion 142 that includes the first andsecond layers of material, such as discussed above. For example, portion142 includes a first layer having an activated surface, with a secondlayer of protective material, such as polyurethane. This allows forpocket abrasion resistance where most lead abrasion can occur. It shouldbe noted that the sealing rings 144 are not affected due to selectiveapplication of the polyurethane coating to the portion 142 (e.g. viamasking). The portion 142 is proximal to the terminal end portion nearthe proximal end of the lead 110. It should be noted that the coating ofmaterial is disposed on an activated surface, as discussed above. Thecoating of a second material such as polyurethane can be disposed on theterminal end in addition to disposing the material along other portionsof the lead.

Advantageously, the activated surface allows for effective coating ofmaterials such as polyurethane to dissimilar materials such as silicone,PTFE, or ePTFE. This allows for new configurations for leads, such ashaving a single component that transitions from a combination ofmaterials, such as silicone and polyurethane, to a single material, suchas silicone. This could reduce the overall number of parts, yet willprovide abrasion resistance. Furthermore, the coating process will allowfor the stiffness to be varied. The processes discussed and claimedherein allow for further manufacturing advantages. For example, theactivation process can be done to a subassembly and stocked for use at alater date. Furthermore, the coatings of materials and combinations ofmaterial allow for a variety of shapes to be formed along the lead. Forexample, a J-shape at the distal end of the lead.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For instance, the leads describedabove include, but are not limited to tachy, brady, or heart failureleads. It should be noted that features of the various above-describedembodiments may be interchanged to form additional combinations. Manyother embodiments will be apparent to those of skill in the art uponreviewing the above description. The scope of the invention should,therefore, be determined with reference to the appended claims, alongwith the full scope of equivalents to which such claims are entitled.

1. A method comprising: activating a surface of a first layer ofmaterial, the first layer of material forming a portion of an insulativelead body extending from a proximal end portion to a distal end portionand having an intermediate portion therebetween; and coating a secondlayer of material on the activated surface of the first layer ofmaterial, including coating a layer of polyurethane along one or moreportions of the first layer of material.
 2. The method of claim 1,wherein activating the surface of the first layer of material includeschemically treating the surface.
 3. The method of claim 2, whereinchemically treating the surface of the first layer of material includesusing a plasma assisted vapor deposition process.
 4. The method of claim3, wherein using the plasma assisted vapor deposition process includestreating the surface of the first layer of material with a monomer. 5.The method of claim 4, wherein treating the surface of the first layerof material with the monomer includes treating the surface with at leastone of acrylic acid, allyl amine, acrylamide, acrylonitrile, methacrylicacid, glycidyl methacrylate, N, N-dimethylacrylamide, or acetylene. 6.The method of claim 1, further comprising cleaning the surface of thefirst layer of material with at least one of O₂, Ar, N₂, CH₃OH, or CF₄.7. The method of claim 1, wherein coating the second layer of materialon the activated surface of the first layer of material includes atleast one of dip coating or spray coating the second layer of materialon the activated surface.
 8. The method of claim 1, wherein coating thesecond layer of material on the activated surface of the first layer ofmaterial includes using a melt process.
 9. The method of claim 1,wherein coating the second layer of material on the activated surface ofthe first layer of material includes coating an outer surface of thefirst layer of material along the one or more portions.
 10. The methodof claim 1, wherein coating the second layer of material on theactivated surface of the first layer of material includes transitioningfrom a layer of only silicone rubber at the lead body distal end portionto a layer of silicone rubber and polyurethane at the lead body proximalend portion or the lead body intermediate portion.
 11. The method ofclaim 1, wherein coating the layer of polyurethane along one or moreportions of the first layer of material includes coating the lead bodyproximal end portion of the first layer of material.
 12. The method ofclaim 1, wherein coating the layer of polyurethane along one or moreportions of the first layer of material includes coating the lead bodyintermediate portion and not the lead body distal end portion.
 13. Amethod comprising: activating a surface of an insulative first layer ofmaterial, the insulative first layer of material extending form aproximal end portion to a distal end portion and having one or morerecesses therein; and coating a second layer of material on theactivated surface of the insulative first layer of material forming alead body, including disposing the second layer of material within aportion of the one or more recesses of the insulative first layer ofmaterial.
 14. The method of claim 13, wherein coating the second layerof material on the activated surface of the insulative first layer ofmaterial includes coating the activated surface with at least one ofpolyurethane or silicone.
 15. The method of claim 13, wherein coatingthe second layer of material on the activated surface of the insulativefirst layer of material includes coating the activated surface with anabrasion resistant material.
 16. The method of claim 13, wherein coatingthe second layer of material on the activated surface of the insulativefirst layer of material includes coating the activated surface with aprotective layer of material.
 17. The method of claim 13, whereincoating the second layer of material on the activated surface of theinsulative first layer of material includes coating the activatedsurface with a lubricious material.
 18. The method of claim 13, whereincoating the second layer of material on the activated surface of theinsulative first layer of material includes coating the activatedsurface with a material having a greater stiffness than the insulativefirst layer of material.
 19. The method of claim 13, wherein disposingthe second layer of material within a portion of the one or morerecesses of the insulative first layer of material includes forming anisodiametric lead body.
 20. A method comprising: activating a surface ofan elongate first layer of material, the elongate first layer includingat least one of silicone rubber, PTFE, or ePTFE, the elongate firstlayer extending from a proximal end portion to a distal end portion andhaving an intermediate portion therebetween; and coating a second layerof material on the activated surface of the elongate first layer ofmaterial to form a lead body, including coating a layer of polyurethanealong one or more portions of the elongate first layer.
 21. The methodof claim 20, further comprising pre-forming the distal end portion ofthe elongate first layer of material and coupling the distal end portionto at least one of the proximal end portion or an intermediate portionof the elongate first layer of material or the second layer of materialusing, at least in part, the activated surface.
 22. The method of claim21, wherein pre-forming the distal end portion of the elongate firstlayer of material includes forming a J-shape distal end portion.
 23. Themethod of claim 21, wherein pre-forming the distal end portion of theelongate first layer of material includes forming a spiral-shape distalend portion.
 24. The method of claim 20, further comprising fixing theelongate first layer of material with the second layer of material usingenergy.
 25. The method of claim 20, wherein coating the second layer ofmaterial on the activated surface of the elongate first layer ofmaterial includes transitioning from a combination of the first andsecond layer of materials to the first layer of material only.
 26. Themethod of claim 20, wherein activating the surface of the elongate firstlayer of material includes providing a non-adhesive based couplingsurface.